The conversion of plant and tree materials to pulp has been a long and well known process for centuries. Numerous processes and systems are known, including for example mechanical processes, chemical processes such as the Kraft process, chemi-mechanical processes, thermo-mechanical processes, and other processes known to those of skill in the art. One value that is measured in the preparation of cellulosic fibers is the curl index. An increase in curl is generally used to indicate an increase in the bulk and absorbency of materials made with the curly fiber.
The goal for producing higher curl index values in pulp processes has been disclosed in several patents. For example, U.S. Pat. No. 6,899,790 involves creating a curly fiber by treating a pulp in a disk refiner at elevated temperatures and pressures. The '790 patent includes shearing the pulp at elevated temperatures and pressures while the pulp is in the refining gap between two plates of a disk refiner. U.S. Pat. No. 7,390,378 discloses treating a fiber under pressure and in the presence of steam in a rotating drum, which batch processes fiber in an enclosed rotating drum. Both patents rely on a thermo-mechanical treatment to convolve the fiber and to produce a higher curl index.